I don't want to open my TeraStation. Is it still possible to become root?

Yes. See the previous question regarding modifying a firmware image and applying it.

As it's possible to make your own (hacked) firmware, the old answers have been removed.

Has anyone successfully replaced the TeraStation's firmware with a different Linux system?

I've chrooted into a Debian/PPC. That works fine once you're root.

I (yvasilev) have successfully installed Gentoo Linux on TeraStation.(How-To will follow soon)

Has anyone successfully recompiled the stock 2.4.20 or any 2.6.x series kernel?

Can I install or replace Linux applications on the TeraStation?

No problem, once you're root.

Can I replace my existing hard drives with larger ones?

Kind of. You need some knowledge of how Linux software RAID works.

To move to larger drives you will have to repartition all 4 new drives in a similar fashion to the existing drives and then copy everything over.

You should be able to follow the instructions on replacing a broken drive in the manual. Replace one drive at a time. You should end up with 4 new drives.

To get the additional space, you need to log in as root, repartition the disks to use all available space and regenerate the data partition RAID. You will lose all your data, but you could use the old disks to make a backup...

A quicker method would be to use a Linux PC and connect all 4 new drives to it when recreating the drive structure along with copying the firmware files.

It might just work with the rescue mode of the 1.07β and newer firmware but I don't have that firmware on my TeraStation, nor do I have enough money to get 4 bigger harddisks to give it a try.

Why should I add a sudoers file, can't I just change the root password?

No, the passwd file is saved and restored during firmware update, so there is no point in changing the root password in a firmware update image as the changes will be ignored.

The sudoers file is not saved and restored, so you can become root this way.